Listen up: Improving neurons for cochlear implants

Hearing loss will affect many of us in our lives. In the US between 25-48 million are currently affected by sensorineural hearing loss. This is typically a result of the loss of hairs in the inner ear which initiates a cascade of secondary events including loss of specialized neurons called spiral ganglion neurons (SGNs) which link these hairs to the brain. Cochlear implants can help restore hearing, but without functional SGNs to integrate the implant with the brain, their performance is limited.

SGNs are differentiated from otic neuronal progenitor cells (ONPs). Transplants of ONPs grown in the lab from a patient’s own cells offer a potential way of fixing the issue. However, cells grown in vitro become adapted to the cell culture dish and can struggle to survive when returned to the patient, particularly when transplanted into the inhospitable environment of the inner ear.

A recent study by scientists working with Akihiro Matsuoka, an ear surgeon at Northwestern University in Chicago, demonstrated the benefits of using a microcrystal slowly releasing the growth factor BDNF as a survival agent for implanted otic neuronal precursor cells in the inner ear. They found transplanted cells can benefit greatly from some help to get themselves established when they are placed in their new environment. Although the number of surviving cells after 90 days was still only about 0.1% of the number transplanted, this was achieved without any immunosuppressant drugs and significantly improved on previous studies by others.

Another noteworthy result of their investigations was the improved quality of ONPs which generated much longer neurite outgrowth. The improvements in survival that these cells achieved following transplant and their improved phenotype demonstrate the benefits of a stable environment in-vitro and supporting cells as they transition from in vitro to in vivo niches.

Picture credit: Aki Matsuoka, Northwestern University.